CHEMISTRY COMMUNITY

Diana A 2L

Ellen Amico 2L wrote:Nope! you can use any of the equations for calculating deltaG. I think it's just a way to label it relating to the reaction.

Thank you! I understand now:)

Diana A 2L

005290099 wrote:Got a corona virus pickup line for all you players out there:

You can't spell quarantine without u, r, a, q, t ;)

THIS WAS A GOOD ONE. THANK YOU.

Diana A 2L

You would calculate the enthalpies of formation of the substances, and then subtract the enthalpy of the reactants from the enthalpy of the products to see if you get a positive or negative value. Negative, it'll be exothermic, positive endothermic.

Diana A 2L

In that case, does that mean cell potentials are calculated first, only using the standard reduction potentials? Like, you calculate cell potential before flipping the equation that is oxidized? Right?

Diana A 2L

The standard cell potential is dependent on how different the concentrations in each of the half-cells are, as that is what generates the potential difference that allows a reaction to proceed in a certain direction. Standard cell potential is zero when the concentrations are the same because the re...

Diana A 2L

^ Yes, also, the overall rate is equal to the forward K / reverse K, so to find the reverse k, you'd have to solve K(reverse)=K(forward)/K(overall).

Diana A 2L

Tauhid Islam- 1H wrote:I'm pretty sure all standard state quantities are dependent on time. Gibb's free energy change is a function of temperature so at different temperatures, you would have different energies.

In that case, how would you calculate Gibbs Free Energy at non-standard temperature?

Diana A 2L

Yall please remember to take care of yourselves, as much as physical health is SO important right now with the corona, don't forget to take care of your mental health. If you ever feel stressed and overwhelmed about the chaos that is 2020, just remember, a wise prophet once said: "It really jus...

Diana A 2L

As the winter quarter comes to a close, I want to congratulate everyone for making it this far. We got through seasonal depression, Kobe's/Gigi's deaths, UCLA's closure and transition to online, and the coronavirus panic over toilet paper. WEVE BEEN THROUGH A LOT THIS YEAR, AND ITS ONLY BEEN 2.5 MON...

Diana A 2L

Does this mean that free energy of activation measured without the enzyme? Or is it needed in relation to the activation energy with the enzyme? Not exactly. It means that the free energy of activation is the, let's say, "left over" energy of activation in addition to the activation energ...

Diana A 2L

Would delta G ionization be the same for other temperatures besides 25 degrees Celsius? Let's say for example you're taking the delta G of ionization for a reaction at 30 degrees Celsius, would you use just the standard equations for delta G? I hope that question makes sense, please someone help I w...

Diana A 2L

I'm glad you guys liked the meme!

Diana A 2L

Also, if heat is released, q is negative, and if it's absorbed, q is positive. Then you use the delta U= q+w equation to determine if overall internal energy is positive or negative.

Diana A 2L

If you take the reverse of a reaction, does the sign of the Ecell also flip, or does it remain? For example, when constructing redox reactions from redox couples you are given, you determine which couple is at the anode and at the cathode by examining Ecell values. You set up the reaction in a way t...

Diana A 2L

Yes! Glad I got the concept. Thank you guys^^

Diana A 2L

Free energy of activation is Gibbs free energy. This is referred to in terms of the energy barrier of a chemical reaction. Activation energy is the energy needed to surpass the barrier of the transition steps of a reaction. The energy of activation is also the difference in energy between the (trans...

Diana A 2L

well we know the ideal gas law inversely relates pressure with volume, pv=nRT, meaning as one increases the other decreases. I haven't seen it being related to le chateliers principle however. Pressure is literally directly related to Le chateliers. Just like a change in volume or concentration aff...

Diana A 2L

Just to lighten the mood and destress:) This one made me laugh out loud.

Diana A 2L

Kaylee Clarke 1G wrote:how would you explain the relationship between cell potential and work in words? and, for cell potential and free energy?

I actually answered a similar question earlier, here’s the link:

viewtopic.php?f=141&t=62264

Hope that helps!

Diana A 2L

The electrochemical series is a table of the relative strengths of oxidizing and reducing agents. It shows the oxidizing and reducing power of redox couples, with the strongest oxidizing agents on the top left and strongest reducing agents at the bottom right. Knowing oxidizing and reducing power he...

Diana A 2L

When delta G is negative, there is energy free to do work. Cell potential wants to go down. IF cell potential goes down there is a release of energy free to do work. I don’t think this is a correct. In the equation delta G= -nFEcell, if cell potential is higher, and more positive, then Gibbs free e...

Diana A 2L

There isn’t a DIRECT relationship between entropy and enthalpy, BUT Gibbs free energy provides a relationship between both terms in the equation: delta G = delta H — T(delta S). For a system where delta G= 0, then delta S= delta H/ T , in which case there is a direct relationship.

Diana A 2L

Kayla Maldonado 1C wrote:
Abby Soriano 1J wrote:The problem will most likely specify which of the steps is the slow step. You will probably be asked if a proposed mechanism matches the observed rate law, but you won't need to actually calculate a value for the slow step.

If the rate matches the observed rate law is that the slowest step?

Yes.

Diana A 2L

Cl 2 (g) \rightarrow HClO(aq) + Cl 2 (g). I don't know how to find the reduction half of this problem, it shows Cl going to Cl which isn't a loss or gain of electrons. I do believe that there is a typo in the book. The Cl2(g) on the product side should be Cl- In that case, the reduction would be fr...

Diana A 2L

^^^ Yes. “Slowness” is relative to the reaction mechanism.

Diana A 2L

Here’s a link to offer a more detailed explanation!

https://chem.libretexts.org/Core/Physic ... _Reactions

Diana A 2L

No, not all zero order reactions is dependent on a catalyst. A zero order reaction could also occur with an enzyme or a surface. It's just that most commonly you would find a catalyst with a zero order reaction. Aren't enzymes just biological catalysts? AHHH yes they are! Let me provide a better an...

Diana A 2L

Sorry I meant a pressure change for one of the reactants or products. I can’t think of any case in which this will happen. In order to change the pressure for a SPECIFIC reactant or product without changing the pressure of the whole system, that reactant or product would have to be isolated. And in...

Diana A 2L

I thought that delta G naught, was just at standard conditions not equilibrium? You’re right the difference is that delta G naught is at standard conditions. Delta G naught is always the same because it is referring to when the reactant/products are at standard conditions. Would that mean standard ...

Diana A 2L

Is it possible to determine a rate law from a tangent line or a secant line of a graph of time in seconds vs concentrations? Essentially you can, but there will be an error bound for the value you find. The only point at which the rate will truly be accurate using a tangent or secant line will be a...

Diana A 2L

You just use the Molarity Values and find K based on concentration. You use whatever you’re given to find K. If given pressure, use pressure. If given concentration, use concentration. Don’t over-complicate it! Good luck!!

Diana A 2L

Can someone explain the relationship between pressure, volume, and le chatelier? Like what if both sides of the equation have equal numbers of moles, how will a pressure change affect that? So if the number of moles is the same, a pressure change won’t affect the equilibrium. Since the pressure wil...

Diana A 2L

Can someone please explain the math steps involved to get the correct answer for this problem? I understand the set up, just not the steps you need to take to get the right answer of 0.42M. Thank you! Well first you’d multiply both sides by -2/0.0257 ( the reciprocal of the constant on the left sid...

Diana A 2L

Could someone help me with number 4 on the UA first review sheet? I am a bit confused as to where to even start with this problem. Q4. The overall dissociation of oxalic acid, H2C2O4 is represented below. The overall dissociation constant is also indicated. a) What volume of 0.400 M NaOH is require...

Diana A 2L

Why is steam a worse burn? is it because it still has higher energy than boiling water at the same temp? Well, steam has a higher energy at 100°C. Let’s visualize. Energy in boiling water is the energy water gained until heating at 100 degrees Celsius to boil. The energy in steam is the energy it g...

Diana A 2L

Can someone please explain (conceptually, not with equations) the relationship between work, cell potential, and delta G? Like explain why wmax is = to delta G. So when delta G is negative, this implies spontaneity (a reaction natural wants to occur in that direction). This means that the reaction ...

Diana A 2L

Do we only use kJ/mol if we have been given the value or calculated a reaction with only one mole of a particular reactant? You use KJ/mol for standard values like standard enthalpy of formation or standard Gibbs free energy because standard conditions are ones for 1 mol of a substance. This is any...

Diana A 2L

How do we determine which step is slow? Or will this always be given? It should be given usually, in the case that it’s not (which could happen), you would pretend every step is the slow one and then find the rate law and check if it matches the overall rate law. Whichever one ends up matching, tha...

Diana A 2L

7A.7 Express the units for rate constants when the concentrations are in moles per liter and time is in seconds for (a) zeroth-order reactions; (b) first-order reactions; (c) second-order reactions. Why do you divide by mol/L for first and second order reactions? The rate of a reaction is usually g...

Diana A 2L

Using the Arrenhius equation, take the natural log. Then you get ln k =-Ea/R (1/T) + ln A. From here, exponentiate, then divide to solve for A. You get A= k/ (e^-Ea/RT), Now to calculate A, you need to know R, T, Ea, and k. We know R, we probably know T, and k, even if it’s not already given, you ca...

Diana A 2L

Are reaction rates only determined by the reactants of the slow step? The reaction rate is determined by the RATE of the slow step, not its reactants. And not all reactions have rate-determining steps. Also, reaction rates are determined by the rate of the slow step only for reaction mechanisms I b...

Diana A 2L

How do you know when to use the average rate vs the unique rate? Unique rates are used when you’re referring to a specific reactant or product, and it’s the rate of disappearance or appearance of a substance divided by the stoichiometric coefficient, which is why it’s so specific. When you calculat...

Diana A 2L

When you're modeling a reaction using the Arrhenius theory, why will the plot be linear? This is because taking the natural log of the Arrhenius equation yields: ln k = ln A - Ea/R(1/T). Then rearranging that gives: ln k = -Ea/R(1/T) + ln A. This equation has the linear form of y=Mx +b. When a reac...

Diana A 2L

Yes. At higher temperatures, molecules move faster and bump into each other more, so essentially kinetic energy will be higher.

Diana A 2L

Yes, because of the equation: delta(G) = delta(G0) + RTln(Q) and since we are at equilibrium, Q=K as well as delta(G0) = -RTln(K). So if you plug things back in, you get delta(G) = -RTln(K) + RTln(K) which equals 0 I thought that delta G naught, was just at standard conditions not equilibrium? You’...

Diana A 2L

You should generally know the molecules for which delta G of formation is zero (the same molecules for which delta H of formation is zero at their standard states).

Diana A 2L

Will concepts of electrolysis (6O) and the process of the corrosion of iron (6N.4) need to be known for the exam?

Diana A 2L

Will average rate and instantaneous rate be the same for a reaction already at equilibrium?

Diana A 2L

For the midterm, do we have to know the equipartition theorem and the contribution to internal energy by translational and rotational energies of particles? This is topic 4B.3, which was in the list of readings for the chapter. Not specified if we must know this or not. Thank you.

Diana A 2L

Is it likely that we will receive an exam question that will require us to actually integrate or apply legitimate math concepts? Is it viable to just memorize the regular and integrated form of the expansion equations, and use appropriate cases? Also, will the work of expansion equations with the in...

Diana A 2L

For the thermodynamic equations used in this class, aren’t most of them constructed in a way that regards work being done BY a system? For example, there’s a negative sign on the work equation to make sure the work value ends up negative since energy is lost from a system when work is done by it. I ...

Diana A 2L

I have a question related to lecture material. Are systems at constant pressure synonymous to systems to which energy changes occur that are reversible? In lecture, there was some sort of association drawn between constant pressure and reversible reactions and I want to confirm if I understood it co...

Diana A 2L

How relevant is this terminology for the exams in this class? What I mean is, will we have to specifically distinguish between what’s extensive or intensive, or is it just to conceptual understanding? It seems unlikely that an exam midterm would be about whether a property is extensive or intensive,...

Diana A 2L

In terms of work and heat equations for energy exchanges between systems and their surroundings, do the equations we went over in Wednesday’s lecture apply to isolated systems? Or do we just not consider energy exchanges for isolated systems at all? IN OTHER WORDS, will we have any isolated system q...

Diana A 2L

For the sake of this course, do we have to know the convention equation from Kp to Kc? And if we do, will it be on Test 1? And if it is, will the equation for it be on the equation sheet? Thank you.

Diana A 2L

In term of understanding the equilibrium constant K, do we have to know the thermodynamic interpretations of it? As in understanding how it relates to Gibbs Free Energy, considering we haven’t really covered Gibbs Free Energy yet.

Diana A 2L

In lecture Professor Lavelle said that you can increase pressure by decreasing volume, but then he also said you can increase pressure in some other way. How else can you increase pressure in a system? Would increasing concentration achieve that based on the comments in this post. Thank you.

Diana A 2L

What is considered an inert gas? Do we have to remember a list of them or is there a way to tell if a gas is inert?

Diana A 2L

I have a question about the conditions required for an “ideal gas”. When something is at standard STATE conditions, which is considered 25 degrees Celsius and 1 atm, does the Ideal Gas Equation apply?

Diana A 2L

When you increase the temperature of an exothermic reaction, it is known to shift left. I understand this fact, but have trouble conceptualizing it and understanding precisely WHY. Why wouldn’t an exothermic reaction with added heat shift right since its inclined to release heat?

Diana A 2L

Does the Ideal Gas Law only apply to scenarios in Standard Temperature and Pressure? (STP) Or can approximations still be made using the Ideal Gas Law Equation with other temperatures within a close range?

Diana A 2L

Are hydrogen bonds a type of dipole-dipole interaction? Lets say for example you're asked to list the types of intermolecular forces a molecule exhibits. If you list hydrogen bonds as one, would you also list dipole-dipole interactions as another?

Diana A 2L

Why are hydrogen atoms bound to Carbon atoms not considered in determining hydrogen binding sites?

Diana A 2L

In this question, it asked to state how many Sigma and Pi bonds are in SO2. The best Lewis structure with the most balanced formal charges has 2 sigma and 2 pi bonds, but there is also a less dominant resonant structure that has 2 sigma and 1 pi bond. In this case, which would be the correct answer?...

Diana A 2L

If a molecule has more ionic character, is it soluble in water? Even if its a covalent bond?

Diana A 2L

When writing a resonance structure, do we do the resonance of the Lewis structure with the best balance of formal charges, or are the structures with imbalanced formal charges that are still correct also count as resonance?

Diana A 2L

Why do P, S, and Cl have expanded octets if they don't have d-orbitals? It doesn't make much sense.

Diana A 2L

I'm a bit confused between the concepts of hydrogen bonding and dispersion. Can someone clarify the difference between the two?

Diana A 2L

Do pi bonds also occur in higher level subshells like the f-subshell? Or is there a different type of bond beyond that?

Diana A 2L

Thank you!

Diana A 2L

I have a question relating VSEPR models with Lewis structures. Knowing what we now know about bonding angles, do we draw Lewis structures also according to bond angles, or does it not matter?

Diana A 2L

Am I understanding this right: the bond order of a compound is the average of all the different bonds present between the individual atoms in the compound. For example, if there's a compound consisting of three atoms bonded by one single and one double bond, you'd take the average bond energy from c...

Diana A 2L

Basically, pi and sigma bonds give you an idea of how electrons from different orbitals are shared within atoms in 3D space. That's really the only significance, and I believe that may be beyond the scope of this chemistry course.

Diana A 2L

why do we need to give bonds a secondary name? what do the names mean? Yeah, why does it matter? It feels like they have no other significance other than giving bonds a new name. the significance of sigma and pi bonds are that they indicate the angles and axis upon which the covalent bonds between ...

Diana A 2L

So for the sake of the Test 2, will we be expected to list the bond angles if we're asked to identify a shape?

Diana A 2L

Hey, I am down for a study group. If anyone wants to form one, email me at dmarut20@gmail.com
And then I'll give you my number:)

Diana A 2L

When we do electron configurations for elements, lets say we get an element like nitrogen with 3p^3 at the end. On the midterm, should we write it as 3p^3 or as px, py, pz?

Diana A 2L

I still don't fully understand. If you're going horizontally across a row does atomic radius increase or decrease? And how about going down a column?

Diana A 2L

Will we be expected to know the shapes and models of orbitals for the midterm? Will a general understanding suffice? I still have trouble envisioning orbital structures in a 3D space just because I've never dealt with the Z-axis before.

Diana A 2L

I don't exactly understand an aspect of the atomic radius trend. Does the atomic radius increase across a row as you keep adding more electrons to the same shell? I know there would be more electron repulsion with lets say flourine rather than boron, so does that cause a radius increase?

Diana A 2L

Will we have to know general electronegativity trends for this upcoming midterm? I haven't fully solidified my concept of it yet and was wondering how much of it will be necessary for the midterm.

Diana A 2L

I like to think of it as the probability of a particles quantum state being dependent on the descriptions of each quantum number. A wavefunction is like the possible position, momentum, and spin of an electron combined. It basically defines an orbital of an electron.

Diana A 2L

In terms of the Hamiltonian in the context of the midterm, the variable itself is given on the formula sheet I believe, so for the purpose of the midterm, all you really have to know is the basic format of the Schroedinger equation: H(wavefunction)=E(wavefunction) and then just plug in the variable ...

Diana A 2L

Are covalent bonds polar or nonpolar? And is there a relation between electronegativity and polarity? I partially forgot my high school chemistry and don't exactly remember what electronegavity is a measure of.

Diana A 2L

Are we going to go over Vespr diagrams and have to learn the different atomic shapes and angles for this class and the final? I am asking because it seems like its going to go hand in had with the bonding properties and resonance stuff we are learning now.

Diana A 2L

Why is it that with some atoms with electrons in the D-orbitals, the S-orbitals will have more energy than the D-orbitals. For example, why would a 4s1 electorn have more energy than a 3d5 electron?

Diana A 2L

Are the shielding effect and electron repulsion synonymous? Does electron repulsion occur as a result of shielding, or are they different concepts?

Diana A 2L

Is there a more significant decrease in nuclear charge as more electrons are being added to the same shell, or as there are more electrons but in energy levels that are further from the nucleus? Basically, I'm asking what the trends in the periodic table are for nuclear charge.

Diana A 2L

Okay that makes sense. But what do you mean by location? Location in terms of which orbital?

Diana A 2L

Are orbitals different from energy levels? The relationship between the two is unclear to me. Are there orbitals within different energy levels? Is whether an electron is located in a certain energy level unrelated to what orbital it is in, or is there a connection between the two?

Diana A 2L

From my understanding, a nodal plane is an area where two or more lobes of a certain type of orbital meet? Is this a valid understanding of it, and also, what is the significance of nodal planes in quantum theory? Is it just to determine the structure of an atom's orbital?

Diana A 2L

Why do energy levels become closer together as the quantum number, n, increases? Why is there such a large gap between the first and second energy levels?

Diana A 2L

This question is quite off topic, but, I was curious, how are the concepts of quantum mechanics are applied to computers? Do the ideas behind quantum-computing originate from the fundamental concepts of the Quantum Theory in H-atoms? Does it go as far back to the basics as that?

Diana A 2L

This is more of a bigger question, conceptual question, but am I understanding this right? Basically, the uncertainty principle and the wave function are both different methods to finding out the locations of electrons in an atom and their distance from the nucleus (or which energy level they are lo...

Diana A 2L

Also, when showing work, do we have to show the work with the overall equations combined, or can we show our work in more of a step by step process? Here's an example: Theres E=hv and C=(lambda)v Here, you can either plug in values individually to derive an answer, or you can combine the equations t...

Diana A 2L

Do ionization energy and threshold energy have the same numerical values? And what is the difference between the two?

Diana A 2L

This is a conceptual question, but is it possible ever to have a frequency of electrons emitted that is different from the values defined by each energy level (n1, n2, etc.), and if it ism in what situation would that happen?

Diana A 2L

For the five homework problems that are due each week for credit, will we receive full credit if we do the five problems all from the same section/topic?

Diana A 2L

Will the midterms and final exams for this class be administered in the discussion period also?

Diana A 2L

I have a conceptual question. For the frequency of a wave, is the frequency a total sum of all of the individual photons of that wave, or is the frequency the amount of energy present in each individual photon?

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